Antigen--antibody reaction investiaged with use of a chemically modified electrode

The antigen-antibody reaction of human choriogenadotropin has been potentiometrically investigated by use of a cyanogen bromide-treated electrode coated with the corresponding anti-serum. The potential of the modified electrode shifts in the positive direction upon contact with a solution of choriogonadotropin. The rate of the reaction at the interface between the electrode and the solution is estimated from the potentiometric measurement to be of the order of 10(4) mol-1 s-1 in diethyl barbiturate buffer, depending to some extent on the rotation speed of the stirrer. The change in potential is almost proportional to choriogonadotropin concentration. It is also pH dependent, the maximum response being at pH 8.7. The technique, applied to samples of human urine, has shown a specific response to choriogonadotropin.